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Effect of reaction conditions on silanisation of sepiolite nanoparticles
Journal of Experimental Nanoscience
Abstract
The study provides insights into the silanisation process of sepiolite nanoparticles. The nanoparticles were modified applying acidic and basic silanisation methods using Methacryloxypropyltrimethoxysilane (γ-MPS) as coupling agent. The silanisation reaction was performed in the following conditions: (1) acidic ethanol–water solution with a pH of 5 and (2) basic cyclohexane with a pH of 9. The influence of the conditions on the surface chemistry of modified particles was then investigated. To characterise the surface of sepiolite nanoparticles, analytical methods such as Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis, X-Ray diffraction (XRD), scanning electron microscopy (SEM), and zeta potential analyses were applied. In addition, the colloidal stability of the modified nanoparticles was studied using a separation analysis. According to XRD and SEM, the basal interlayer distance of pristine sepiolite is not altered by silanisation process. TGA reveals that the grafting percentage of organosilane synthesised by basic method is approximately two times of that of acidic method. The silane coverage on the surface of the sepiolite and the per cent of hydroxyl groups covalently bound to γ-MPS were calculated. Separation analysis indicates decline in dispersion stability of the modified nanoparticles in ethanol due to increment of their hydrophobicity.
... As expected, the characteristic bands of SFG particles are very similar to those of sepiolites. other bands at 1206, 1065 (shoulder) and 964 cm −1 due to Si-O bonds, and bands at 682 and 641 cm −1 coinciding with Mg-OH bond vibrations [39][40][41]. ...
... The band at 1695 cm −1 coincides with the bending movement of the water adsorbed on the surface of the sepiolite, whereas the band at 1659 cm −1 is attributed to the flexural vibrations of zeolitic water. The 1200-400 cm −1 range is characteristic of silicates: an absorption centered at 1016 cm −1 due to the Si-O-Si vibration, other bands at 1206, 1065 (shoulder) and 964 cm −1 due to Si-O bonds, and bands at 682 and 641 cm −1 coinciding with Mg-OH bond vibrations [39][40][41]. The thermal stability of the SFG particles was evaluated by TGA. ...
... Therefore, the loss of mass from the SFG particles should exclusively be due to the degradation of the nanosepiolites modified with silane groups. The three steps clearly displayed in the thermogram of the SFG particles are very similar to those observed in the thermograms of sepiolites [39,41,43]. The mass loss in the SFG particles and that in sepiolites are analogous, and must therefore be based mainly on the evaporation of the modifier added to the sepiolites (silane groups) as well as on the evaporation of the water contained in the sepiolites: zeolitic water, surface-adsorbed water and coordinated water. ...
In the present study, a promising flame retardant consisting of 80 wt% silane-modified nanosepiolites functionalized with 20 wt% graphite (SFG) is used to obtain a synergistic effect principally focussed on the thermal stability of water-blown rigid polyurethane (RPU) foams. Density, microcellular structure, thermal stability and thermal conductivity are examined for RPU foams reinforced with different contents of SFG (0, as reference material, 2, 4 and 6 wt%). The sample with 6 wt% SFG presents a slightly thermal stability improvement, although its cellular structure is deteriorated in comparison with the reference material. Furthermore, the influence of SFG particles on chemical reactions during the foaming process is studied by FTIR spectroscopy. The information obtained from the chemical reactions and from isocyanate consumption is used to optimize the formulation of the foam with 6 wt% SFG. Additionally, in order to determine the effects of functionalization on SFG, foams containing only silane-modified nanosepiolites, only graphite, or silane-modified nanosepiolites and graphite added separately are studied here as well. In conclusion, the inclusion of SFG in RPU foams allows the best performance to be achieved.
... To make the filler compatible with the hydrophobic polymer matrix, partial or complete surface hydrophobization/functionalization of the particles through different mechanisms, e.g. adsorption, ion exchange with organic/inorganic cations, and silanization have been considered (Mazloom Jalali et al., 2016. In silanization, as a low-cost and effective surface treatment technique, the organic molecule is covalently bonded onto the particles surface via condensation reaction between silane molecule and surface hydroxyl groups which results in formation of strong Si-O-Si bonds (Gun'ko and Turov, 2013;Gun'ko, 2019). ...
... Taking into account the silanol group density on fumed silica (2.5 groups per nm 2 ) (Evonik, 2015) and by assuming that each γ-MPS reacts with one silanol group, the percentage of hydroxyl groups covalently bound to γ-MPS is calculated as 43.2% for BF and 39.2% for AF. The calculations were performed according to our previous work (Mazloom Jalali et al., 2016). Sedimentation behavior of PF, AF, and BF in ethanol is depicted in Fig. 3. ...
... The absorption of carbonyl vibration with hydrogen bonding appears at about 1700 cm -1 while it appears around 1720 cm -1 without hydrogen bonding. For sample AF, the aforementioned peak observed at 1702 cm -1 is related to carbonyl vibration with the hydrogen bonding while in the case of BF, this band at 1717 cm -1 are assigned to carbonyl vibration without hydrogen bonding (Mazloom Jalali et al., 2016. ...
A facile procedure has been devised to develop a novel dentin bonding system containing poly (acrylic acid)-grafted-silanized fumed silica particles as reinforcing filler, with high stability of nanoparticle dispersion and enhanced bond strength and mechanical properties. In the first step, the silanization of fumed silica nanoparticles was performed in the following conditions: (i) ethanol-water solution with a pH of 5 and (ii) cyclohexane with a pH of 9 using trimethoxysilylpropyl methacrylate (γ–MPS) as a reactive silane coupling agent. FTIR and TGA analyses confirmed the presence of silane in the resultant structure and enhanced dispersion stability of modified particles was proved by a separation analyzer and also zeta potential analyses. In the second step, free radical polymerization of acrylic acid monomers in the presence of silanized nanoparticles was carried out and poly (acrylic acid) -grafted- silanized fumed silica were acquired. The flexural strength and fracture toughness of the adhesive containing 0.2 wt.% of the dual modified filler reached maximum of 70.4 MPa and 1.34 MPa m1/2, respectively, showing average improvements of 74% and 179%, respectively, in comparison with the adhesive without filler. Flexural modulus values did not significantly change with increasing the filler content except the adhesive containing 5 wt.% having the lowest flexural modulus. The highest microtensile bond strength was also observed at 0.2 wt.% filler content showing the average improvements of 197% as compared with the neat adhesive. Energy dispersive X-ray (EDX) mapping confirmed a homogenous and uniform distribution of the fillers in the adhesive matrix containing 0.2 wt.% and 0.5 wt.% of filler while incorporation of 5 wt.% led to large particle aggregates. SEM images of the fracture surface of the adhesive with different filler contents subjected to fracture toughness test showed rougher surface and longer crack path by increasing filler concentration. The adhesive containing 0.2 wt.% of filler perfectly penetrated into the dentin tubules proved by the SEM micrographs in microtensile bond strength test.
... Herein, a fluorine-free superhydrophobic coating with high flexibility was prepared based on modified sepiolite powder and EP. EP are used as polymers and incorporate hydrophobic materials to enhance the durability and robustness of hydrophobic coatings [54]. Therefore, the simple and green hydrophobic modification of traditional EP coatings with nano-fillers is novel. ...
In this work, a superhydrophobic coating was developed by modifying pure epoxy resin with prepared sepiolite powder. The wettability, morphology, and composition of the superhydrophobic coating were characterized by contact angle measurement (CA), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). The corrosion behavior of the coatings was investigated by electrochemical impedance spectroscopy (EIS), salt-spray test, and Scanning Kelvin Probe (SKP). The results showed that the composite coating had better corrosion performance than pure epoxy resin (EP) coating, and the composite coating showed super-hydrophobicity with a contact angle of 154.6º and a sliding angle of 3ºafter sprayed with 5 wt. % modified powder. The corrosion region of the damaged coating could be obviously restricted and the corrosive rate of the substrate was delayed and confirmed by SKP technology. The complete coating morphology was more conducive to enhancing the corrosion resistance of the sample.
... The surface charge of the sepiolite after silanization with the organosilane agents was determined by zeta potential measurements. The isoelectric point (IEP) of this sepiolite is 2.7 (Jalali et al. 2016), and so its surface was negative at the pH of the suspension. After grafting with the organosilanes with the exception of APTES, the surface potentials were more negative and similar which was not related to the pH of the suspensions given their more acidic character. ...
The increased detection of pharmaceuticals in finished drinking water has become a growing cause of concern in recent years. The removal of atenolol, ranitidine, and carbamazepine by sepiolite, following functionalization of its surface by organosilane grafting, constituted the subject of this investigation. Silylated surfaces include octyl, γ-aminopropyl, 3-chloropropyl, and triphenyl moieties. The sorption of atenolol and ranitidine was higher on sepiolite functionalized with 3-chloropropyl, while carbamazepine showed a higher sorption on sepiolite with triphenyl groups. Filtration experiments of both ranitidine and carbamazepine on octyl- and triphenyl-sepiolite, respectively, showed a higher retention of ranitidine in comparison to carbamazepine, in spite of the fact that the number of sorption sites was lower due to its higher binding rate.
... On the other hand, for PHA1005 matrix, T1 presents some agglomerates, which in principle should be avoided due to the aminosilane modification. At times, the greater the amount of organic modifier in nanoclays, the greater the impediment to debundle [35] and this might be the behaviour observed between T1 (modified) and T2 (natural) for this matrix. ...
Polyhydroxyalkanoates (PHAs) are nowadays considered competent candidates to replace traditional plastics in several market sectors. However, commercial PHA materials exhibit unsatisfactory smells that can negatively affect the quality of the final product. The cause of this typical rancid odour is attributed to oxidized cell membrane glycolipids, coming from Gram-negative production strains, which remain frequently attached to PHAs granules after the extraction stage. The aim of this research is the development of customised PHA bio-nano-composites for industrial applications containing organomodified nanoclays with high adsorbance properties able to capture volatile compounds responsible for the displeasing fragrance. To this end, a methodology for the detection and identification of the key volatiles released due to oxidative degradation of PHAs has been established using a headspace solid-phase microextraction technique. We report the development of nine bio-nano-composite materials based on three types of commercial PHA matrices loaded with three species of nanoclays which represent a different polar behaviour. It has been demonstrated that although the reached outcoming effect depends on the volatile nature, natural sepiolite might result in the most versatile candidate for any the PHA matrices selected.
... On the one hand, analysing PHA3002 micrographs, T2 seems to appear better dispersed of organic modifier in nanoclays, the greater the impediment to debundle [44] and this 335 might be the behaviour observed between T1 (modified) and T2 (natural) for this matrix. ...
Poly(hydroxyalkanoates) (PHAs) are currently considered competent candidates to replace traditional plastics in several market sectors. However, commercial PHA grades exhibit unsatisfactory smell that can negatively affect the quality of the final product. The cause of this typical rancid odour is attributed to oxidized cell membrane glycolipids, coming from Gram negative production strains, which remain frequently attached to PHAs granules after extraction. The aim of this research is the development of customised PHA nano-biocomposites for industrial applications containing organo-modified nanoclays with high adsorption properties able to capture volatile compounds responsible of the displeasing fragrance in PHAs. To this end, a methodology for the detection and identification of the key volatiles released due to oxidative degradation of PHAs has been established using a headspace solid-phase microextraction technique. We report the development of nine nano-biocomposite materials based on three types of commercial PHA matrices loaded with three species of nanoclays which represent a different polar behaviour. It has been demonstrated that although the reached outcome effect depends on the volatile nature, natural sepiolite (T2) might result in the most versatile candidate for all PHA matrices selected.
... The diffraction patterns of T1 and T2 shows the expected structure for sepiolite organoclays, with the principle peak being at 2θ = 7.29, showing highest intensity. Results agree with those of Penning et al. as the basal interlayer distance of pristine sepiolite seems not to be altered by the silanisation process [77], and as the authors had corroborating calculations for the basal distance for d(1,2,1) and d(1,2,0), respectively (see Table 3). In addition, T3 presents three well-differentiated peaks at 2θ = 14.03, 19.83 and 61.9, which are typical of montmorillonite organoclay. ...
Microplastics have become one of the greatest environmental challenges worldwide. To turn this dramatic damage around, EU regulators now want to ensure that plastic itself is fully recyclable or biodegradable. The aim of the present work is to develop a biobased and biodegradable biocomposite based on commercial polyhydroxyalkanoates (PHAs) and nanoclays, with the objective of achieving a reduction of rancid odour while avoiding any loss in thermomechanical properties, thus tackling two key disadvantages of PHAs. This research aims at completely characterising the structural, thermal and mechanical behaviour of the formulations developed, understanding the compatibility mechanisms in order to be able to assess the best commercial combinations for industrial applications in the packaging and automotive sectors. We report the development of nine nanobiocomposite materials based on three types of commercial PHA matrices: a linear poly(3-hydroxybutyrate) (P3HB); two copolymers based on poly(3-hydroxybutyrate)-co-poly(4-hydroxybutyrate) (P3HB-co-P4HB); and nanoclays, which represent a different polar behaviour. Dispersion achieved is highly relevant compared with literature results. Our findings show impressive mechanical enhancements, in particular for P3HB reinforced with sepiolite modified via aminosilanes.
... In contrast, sepiolite (Mg4Si6O15(OH)2•6H2O) is a novel material in the context of BMI chemistry. It is a rod-shaped, mineral clay consisting of an octahedral magnesium layer sandwiched between two silica tetrahedral layers [ 27 ]. The organoclays used here (Pangel B20 and B40) are modified by adsorbing quaternary ammonium surfactants to the particle surface. ...
Rod-like sepiolite organoclays are incorporated into a simple, first-generation commercial bismaleimide (BMI) to improve the inherent brittleness of the cured polymer; montmorillonite clay is used as a baseline comparison. Both solution and solid state blending methods are evaluated to determine which offer the best method of dispersion. Increased Pangel B40 (sepiolite) loading leads to finer particle sizes and a narrower size distribution indicating that the nanoclay assists the grinding and particle size refinement. The cured nanocomposites containing sepiolite nanoclays offer superior storage modulus to the montmorillonite. Introduction of Pangel B40 achieves around a 15–42% increase in plane-strain fracture toughness (depending on loading) and modest increases (+2%) in char yield when compared with the unmodified BMI.
... In addition, the characteristic vibration of Si-O-Si appears at 979 cm À1 as a strong and sharp band. [108] Stretching vibrations of Si-O-Si bonds in the tetrahedral sheets of sepiolite appear at 1201 and 1078 cm À1 [109][110][111] (Fig. S1, see Supplementary Material). ...
Nanofibre sepiolite catalyzed the rapid, clean, and highly efficient synthesis of 2-amino-4H-chromene derivatives by a one-pot, three-component condensation of a series of aldehydes, various enolizable C-H bonds (such as dimedone, α-naphthol, resorcinol, and 4-hydroxy-2H-chromen-2-one), and malononitrile in a mixture of water/ethanol. The present method offers several advantages such as high to excellent yields, short reaction times, mild reaction conditions, simple procedure, use of inexpensive, non-toxic, and naturally available catalyst, easy isolation of the products, and no need for column chromatography. The catalyst could be easily separated from the reaction mixture and can be reused for many consecutive trials without a significant decline in its reactivity.
This work describes the effect of functionalized silica, treated with organosilane (γ‐methacryloxypropyltrimethoxysilane), on the wettability loss of polypropylene (PP) film when exposed to surface oxidization treatment by atmospheric air plasma. The observed wettability loss results from the spontaneous process within the polymer matrix, which reduces surface energy, causing oxidized polymer molecules to move toward the bulk of the film. The effect of silica's functionalization on the initial wettability of oxidized PP film and its loss on storage time is measured by contact angle. Elemental analysis of the modified silica, employing acid catalytic processes, reveals the highest functionalization yield. Silicon nuclear magnetic resonance shows that the post‐condensation process negatively affects structures formed by the organosilane, eliminating three‐dimensional bonds and reverting it to its original and hydrolyzed state. The solvent extraction process and elemental analysis confirm that the concentration of organosilane in the chemically bonded layer, which was around 9 wt%, is not influenced by the post‐condensation treatment. Notably, silica functionalized with the highest concentration of organosilane has significantly improved initial wettability when oxidative treatment occurs within a shorter residence time (30 s), which achieved a contact angle of 53.8° against 59.1° for the film with untreated silica. However, the wettability loss rate of the materials remains unaffected by the presence of functionalized silica.
Eskisehir sepiolite (SEP) was given a hydrophobic surface through acid treatment followed by silanization. The silanization process was realized with trimethoxy(octadecyl)silane (TMODS), (3-aminopropyl)triethoxysilane (APTES) and (3-glycidyloxypropyl)trimethoxysilane (GPTMS) coupling agents. The effects of temperature and reaction time on the silanization degree were studied within the ranges 25–50°C and 2–48 h, respectively. The efficiency of silanized SEP as an oil absorbent was investigated in pure olive oil media. The structural changes in sepiolite samples were monitored by X-ray diffraction (×RD), N2 adsorption (BET), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), and Fourier Transform Infrared spectroscopy (FTIR). Accordingly, maximum organic loading was achieved as 20.6% (w.) corresponding to 0.69 mmol silane/g SEP, when silanization was conducted with TMODS at 50°C for 24 h. Acid activation with hydrochloric acid removed the dolomite fraction and thus was in favor of silanization. The oil uptake capacities followed the order: GPTMS modified acid-activated SEP > APTES modified acid-activated SEP> TMODS modified acid-activated SEP > acid-activated SEP > SEP reaching as high as 2.77 ± 0.01 g/g at utmost. The augmentation in oil uptake capacity was not solely related to increased hydrophobicity, but also to altered surface area and porosity. Absorbed oil was recoverable at nearly 90% after three absorption – desorption cycles.
The main objective of this work is to compare the effectiveness of a newly synthesized glut palmitate (GP) salt and a commercially available (3-aminopropyl) trimethoxysilane (APTMS) as coupling agents in sepiolite (SEP) filled ethylene propylene diene monomer (EPDM/SEP) composites. The unmodified and modified composites with different amounts of SEP were prepared with an open two-roll mill and the morphology, cure characteristics, tensile properties, flammability, and thermal stability were studied. Fourier transform infrared spectroscopy (FTIR) analysis indicated shifting of the related absorption peaks and confirmed the interaction between composite with the GP salt and APTMS and the successful modification of sepiolite particles in EPDM/SEP composites. The maximum torque (MH), scorch time (ts2) and cure time (t90) of the modified EPDM composites decreased with both coupling agents. Thermal stability reduced in the presence of coupling agents but the reduction is more pronounced in the composite with GP salt due to low-temperature degradation of the fatty acid. Compared with unmodified EPDM/SEP, the tensile strength of the modified EPDM/SEP with GP and APTMS enhanced by 15% and 52%, respectively but both elongation at break and modulus were lowered. GP and APTMS were efficient coupling agents in linking the SEP and EPDM matrix, reducing the rubber-filler interaction (Qf/Qg) from 1.00 for the EPDM/SEP composites to 0.76 and 0.64 for the EPDM/GP/SEP and EPDM/APTMS/SEP composites, respectively.
Cyclohexanone‐formaldehyde resin and acetophenone‐formaldehyde resin were in situ modified with sodium alendronate and the nanocomposites of cyclohexanone‐formaldehyde resin with sepiolite and montmorillonite by adding the nanoclay into the resin formation media. The analysis of nanocomposites of nanoclay in the resin were carried out with X‐ray diffraction. Exfoliated nanocomposites containing as much as 5 wt% sepiolite were obtained while the nanocomposites of montmorillonite were intercalated. The nanocomposites of alendronic acid‐modified ketone‐formaldehyde resin containing as much as 20 wt% sepiolite or 10 wt% montmorillonite were successfully produced in situ. Fourier transform infrared and nuclear magnetic resonance spectroscopies (NMR) were used for the structural characterization of the modified resins. The alendronic acid modified resins and their nanocomposites with the clays were used to produce reactive non‐toxic fire retardant rigid polyurethane foam. The polyurethane foam containing alendronic acid‐modified acetophenone‐formaldehyde resin had a residue of 20% in the thermogravimetric analysis and was HB‐grade in the horizontal fire test (HB) and self‐extinguished in about 3–5 s during the test. Polyurethane foams containing alendronic acid and the nanoclay with the limiting oxygen index value of 20.8 were achieved.
Objective
In this study, we incorporated hybrid nanoparticles (poly (acrylic acid)-grafted nanoclay/nanosilica, respectively, with platelet and spherical morphologies, abbreviated as PAA-g–NC–Sil) in different concentrations (0, 0.2, 0.5, 1, 2 and 5wt.%) to an experimental dentin bonding system and investigated the physical properties of the filled adhesive and its shear bond strength (μ-SBS) to dentin. We subsequently compared the properties of the adhesives containing PAA-g–NC–Sil with previously studied adhesives containing poly(methacrylic acid)-g-nanoclay (PMA-g-NC) (Solhi et al., 2012a), poly(acrylic acid)-g-nanoclay (PAA-g-NC) (Solhi et al., 2012b), and the hybrid poly(methacrylic acid)-grafted-nanoclay-nanosilica (PMA-g–NC–Sil) (Solhi et al., 2020).
Materials and methods
In a set of previous publications and the present paper, we grafted poly (acrylic acid) (PAA) or poly(methacrylic acid) (PMA) onto the surface of pristine Na-MMT nanoclay (Cloisite® Na⁺) through free radical polymerization of monomer in an aqueous media in the presence or absence of nanosilica particles. We characterized the resulting modified nanoparticles (PMA-g-NC, PAA-g-NC, PMA-g–NC–Sil and PAA-g–NC–Sil) using GPC, FTIR, TGA, and XRD. We then incorporated the modified particles as functionalized fillers to experimental dentin adhesives in different concentrations and studied the stability of modified fillers dispersion by separation analysis. We also studied the properties of the photo-cured adhesive matrices using FTIR, TEM, SEM, EDXA, and XRD. We examined the shear bond strength of the adhesives (containing different contents of each modified filler, separately) to human premolar teeth. The results were analyzed and compared statistically.
Results
The results confirmed that the polymers have been grafted onto the surface of nanoclay. An exfoliated structure for the nanoclay platelets in the photo-cured adhesive containing PAA-g–NC–Sil was observed. Addition of 0.5 wt.% of PAA-g–NC–Sil to the experimental adhesive increased the shear bond strength and the dispersion stability in comparison to unfilled adhesive. The same trend was also observed for adhesives containing PMA-g-NC, PAA-g-NC, and PMA-g–NC–Sil. The adhesive containing PAA-g–NC–Sil showed the best dispersion stability and subsequently the highest shear bond strength in the optimal concentration among adhesives containing the four available fillers (PMA-g-NC, PAA-g-NC, PMA-g–NC–Sil and PAA-g-NC).
Significance
Addition of poly (acrylic acid) modified nanoparticles to the experimental dentin adhesives resulted in higher shear bond strength due to the potential interactions between the carboxylic acid functional groups on the surface of the modified particles and the dentin structure. Between the poly (acrylic acid) and poly (methacrylic acid), the former acid with higher PKa performed better. Addition of the spherical nanosilica particles to the adhesives containing platelet nanoclay helped to better exfoliate the platelets resulting in improved μ-SBS and dispersion stability.
The aim of this study was to synthesize acrylic core-shell particles and silica-loaded core-shell hybrid particles through emulsion polymerization. Also this work examined the influence of synthesized nanoparticles loading in a Bis-GMA/TEGDMA resin matrix on some mechanical properties of the dental composite resins. Core-shell particles consisting of polybutyl acrylate (PBA) rubbery core and polymethyl methacrylate (PMMA)/polystyrene (PS) shell were synthesized by seeded emulsion polymerization. For preparing the core-shell hybrid particles, first silica particles with diameters of about 68 nm were synthesized based on the Stöber process. Then the surface of silica particles was treated with ɣ-MPS. Afterwards, polymeric shell was coated on silica nanoparticles through emulsion polymerization. The morphology of core-shell particles was examined by SEM/TEM. Mechanical properties (fracture toughness, flexural strength and flexural modulus) of the photo-cured Bis-GMA/TEGDMA dental resins/composites filled with different mass fractions of synthesized nanoparticles were tested, and analysis of variance (ANOVA) was used for the statistical analysis of the acquired data. Formation of glassy shell on PBA core in core-shell particles, grafting of ɣ -MPS onto the silica particles and encapsulation of modified silica by polymeric shell in core-shell hybrid particles were confirmed using various analytical techniques. The results of mechanical tests showed that fracture toughness of Bis-GMA/TEGDMA dental resins improved about 35% by the inclusion of 5 wt% silica-loaded core-shell hybrid particles with little effect on flexural strength. This study shows that incorporation of proper amount of hybrid core-shell particles in dental composites can improve their fracture toughness and thus may extend their service life.
Objective
In this study the mechanical and adhesion properties of an experimental methacrylate based dentin bonding system containing a combination of spherical and layered platelet nanoparticles were investigated. The nanoparticles were first modified through surface graft polymerization of methacrylic acid in order to make the particles surface compatible with the bonding matrix resin.
Materials and methods
Graft free radical polymerization in aqueous media was performed to attach Poly (methacrylic acid) (PMA) chains onto the surface of Na-MMT nanoclay (Cloisite® Na+) and silica nanoparticles (Aerosil® 200). The hybrid PMA grafted nanoparticles (PMA-g–NC–Sil) were characterized using GPC, FTIR, TGA, and X-ray diffraction (XRD). Dentin adhesives containing different amounts of the hybrid modified nanoparticles were photopolymerized and their characteristics were studied using FTIR, TEM, SEM, EDXA, and XRD techniques. The adhesives containing different amounts of PMA-g–NC–Sil were applied to the conditioned human premolar dentin to bond a dental composite to the teeth. The bond strength was then measured by microshear bond strength testing method. The results were analyzed and compared statistically. The stability of PMA-g–NC–Sil dispersion in the dentin adhesive was investigated using separation analysis (LUMi Reader) techniques.
Results
The grafting of PMA chains onto the surface of nanoclay was confirmed by FTIR and TGA analytical techniques. The intercalated-exfoliated structure for the nanoclay platelets in the photo-cured adhesive was observed using XRD and TEM. The surface modification of the nanoparticles significantly increased the dispersion stability of the fillers in the adhesive solution. The microshear test results indicated that the incorporation of the PMA-g–NC–Sil nanoparticles significantly enhanced the bond strength to dentin with the highest shear bond strength observed at 0.5 wt.%.
Significance
The incorporation of the PMA modified hybrid nanofillers into the dentin adhesive resulted in a dentin bonding agent with enhanced shear bond strength through reinforcing the adhesive matrix and potential interactions between their carboxylic acid groups and the tooth structure. The dispersion stability of the nanoparticles was also dramatically improved by the surface modification of the nanoparticles.
Hydrophobic surfaces have potential to enhance the efficiency of a plethora of applications, from heat exchangers, to underwater structures, to food industry and oil-water filtration. A large fraction of currently available hydrophobic coatings consists of perfluorinated compounds or organosilane-based chemistries, both of which can be toxic and bioaccumulate in nature. Here, we develop environment-friendly and economical superhydrophobic coatings using naturally abundant sepiolite nanoparticles functionalized with naturally extracted fatty acids from cinnamon and myristica. We demonstrate our coating on a variety of metallic and non-metallic surfaces with dip coating of aluminum, adsorbent fabrics, glass and even paper. Contact angle measurements revealed the ability to scalably produce high apparent advancing contact angles (> 160°) with low contact angle hysteresis (< 5°). We characterized our coated surfaces for their anti-biofouling characteristics using Gram negative and Gram positive bacteria. The results showed that the bacterial attachment considerably decreased (< 5%) compared to the untreated surfaces (≈30%), resulting in lower biofouling. The chemical, mechanical, and thermal durability of the coating were studied, with results showing that immersing the samples in different pH aqueous solutions (4 ≤ pH ≤ 10) and different temperatures (T < 300°C) for various times does not have significant effect on the superhydrophobicity of the samples. Our work not only presents the development of a naturally-derived and environment-friendly superhydrophobic anti-biofouling coating, it demonstrates a pathway for future research on the development of sustainable and ecological functional coatings.
For the first time, a ternary hybrid system composed of halloysite nanotubes, HNTs, cyclodextrin nanosponges, CDNS, and g-C3N4 is prepared and used for immobilization of Pd(0) nanoparticles and development of a heterogeneous catalyst, [email protected]3N4 for promoting ligand and copper-free Sonogashira and Heck coupling reactions in aqueous media. HNT as a porous tubular clay with outstanding thermal, mechanical and textural properties can act as a support for immobilizing Pd nanoparticles. The role of CDNS can be explained on the base of its capability to form inclusion complexe with substrates and bringing them in the vicinity of the catalytic active sites. Regarding the role of g-C3N4 in catalysis, it is proved that its presence can suppress the Pd leaching dramatically. The contribution of each component as well as synergistic effect between them results in high catalytic activity and recyclability (up to 10 reaction runs) of the catalyst.
Taking advantage of the properties of polyacrylamide (P), the capability of cyclodextrin (CD) to form inclusion complex and outstanding features of halloysite nanoclay as catalyst support, a ternary hybrid system, Hal-P-CD, was designed and synthesized through growing polyacrylamide on the surface of functionalized halloysite nanotubes followed by introduction of β-cyclodextrin. The hybrid system was successfully used for immobilization of Pd nanoparticles and formation of a heterogeneous catalyst, [email protected] The structure of [email protected] Hal-P-CD was confirmed by using SEM/EDS, TEM, XRD, BET, ICP-AES, TGA, FTIR and elemental mapping analysis and its catalytic activity was studied for promoting ligand and copper-free Sonogashira coupling reaction in aqueous media (1:1 mixture of water and ethanol). The results established that [email protected] could catalyze the coupling reaction to afford the desired products in high yields and short reaction times. Notably, the catalytic activity of [email protected] was superior to those of [email protected] and [email protected] The study of the reusability of the catalyst up to 7 reaction runs as well as Pd leaching confirmed the heterogeneous nature of the catalysis and the efficiency of Hal-P-CD for suppressing the Pd leaching. Additionally, this catalyst could also be successfully used for promoting Heck coupling reaction.
MODIFICATION OF SEPIOLITE BY TREATMENT WITH FLUORIDES:
STRUCTURAL AND TEXTURAL CHANGES
Maria Jesús Belzunce1,Sagrario Mendioroz1 and Jerzy Haber2
I Instituto de Catálisis y Petroleoquímica, CSIC, Campus de la UAM, Cantoblanco, 28049 Madrid, Spain
2 Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek,30239 Kraków, Poland
Abstract-
In the search for new applications of natural silicates, various F- treatments have been applied to sepiolite to increase its acidic properties and for use as a catalyst in reactions occurring via carbonium ions. Two types of treatments including hydrofluoric acid (HF) at different concentrations and 2 N NH4F have been utilized and the physicochemical characteristics of the resulting mâterials studied using standard techniques. The X-ray diffractogram (XRD) patterns indicate a decrease in crystallinity of the original
material as well as the appearance of amorphous silica. SEM micrographs showed a shortening and aggregation of the sepiolitic fibers. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), thermogravimetric analysis/differential thermal analysis (TGA,/DTA), N, adsorption-desorption isotherms and Hg intrusion were used to study the changes occuning in the structure, surface area and pore distribution of samples and acidity was evaluated by IR and thermoprogrammed desorption (TPD) of adsorbed ammonia and pyridine. It was found that acidity increased in most of the samples after anionic and cationic interchange between the activating agents and the surface sites, or extralattice cations.
Additionally, structural changes induced by treatments modified the Brönsted and Lewis acidity. Mild treatments with ammonium fluoride are more effective than HF treatments in acidity generation.
Key Words-Activation, Fluoride Activation, Sepiolite, Silicate Acidity.
Clay mineral-containing nanocomposite hydrogels have been proven to have exceptional composition, properties, and applications, and consequently have attracted a significant amount of research effort over the past few years. The objective of this paper is to summarize and evaluate scientific advances in clay mineral-containing nanocomposite hydrogels in terms of their specific preparation, formation mechanisms, properties, and applications, and to identify the prevailing challenges and future directions in the field. The state-of-the-art of existing technologies and insights into the exfoliation of layered clay minerals, in particular montmorillonite and LAPONITE®, are discussed first. The formation and structural characteristics of polymer/clay nanocomposite hydrogels made from in situ free radical polymerization, supramolecular assembly, and freezing-thawing cycles are then examined. Studies indicate that additional hydrogen bonding, electrostatic interactions, coordination bonds, hydrophobic interaction, and even covalent bonds could occur between the clay mineral nanoplatelets and polymer chains, thereby leading to the formation of unique three-dimensional networks. Accordingly, the hydrogels exhibit exceptional optical and mechanical properties, swelling-deswelling behavior, and stimuli-responsiveness, reflecting the remarkable effects of clay minerals. With the pivotal roles of clay minerals in clay mineral-containing nanocomposite hydrogels, the nanocomposite hydrogels possess great potential as superabsorbents, drug vehicles, tissue scaffolds, wound dressing, and biosensors. Future studies should lay emphasis on the formation mechanisms with in-depth insights into interfacial interactions, the tactical functionalization of clay minerals and polymers for desired properties, and expanding of their applications.
The performance and service life of glassor ceramic-filled polymeric composites depend on the nature of their resin, filler and interfacial phases as well as the efficacy of the polymerization process. The synergy that exists between the organic polymer matrix and the usually inorganic reinforcing filler phase is principally mediated by the interfacial/interphasial phase. This latter phase develops as a result of the dual reactivity of a silane coupling agent, (YRSiX 3), a bifunctional molecule capable of reacting with the silanol groups of glass or ceramic fillers via its silane functional group (-SiX 3) to form Si-O-Si- bonds to filler surfaces, and also with the resin phase by graft copolymerization via its Y functional group, usually a methacrylic vinyl group. In this paper, we explore some of the chemistry of organosilanes, especially that of functional organosilanes (or silane coupling agents as they are commonly known) that are used to mediate interfacial bonding in mineral reinforced polymeric composites. The chemistry of organosilanes can be quite complex involving hydrolytically initiated self-condensation reactions in solvents (including monomers) that can culminate in polymeric silsesquioxane structures, exchange reactions with hydroxylated or carboxylated monomers to form silyl ethers and esters, as well as the formation of silane derived interfaces by adhesive coupling with siliceous mineral surfaces.
We report the sol–gel preparation of SiO2/montmorillonite composite materials and the investigation of the effect of the amount of clay and the TEOS concentration on the textural and structural properties of the composites. Pre-swelling of the clay with cetyltrimethyl ammonium results in solids with a larger mesoporous surface area. A decrease in the gel time and an increase in the surface area were observed upon increasing the amount of clay in the reaction medium. These porous solids showed acidic properties, and their acidities were correlated with the amount of the clay mineral. The obtained composites were functionalized by adding manganese, and their catalytic properties were evaluated in the cyclohexene oxidation reaction.
Graphical Abstract
In this work, the silylation of sodium montmorillonite (Na+-Mt, Nanofil 757®) was performed using (3-aminopropyl)triethoxy silane (APTES). Different reaction conditions were used varying the reaction time and the amount of the aminosilane. Epoxy-based nanocomposites were prepared with different amounts of silylated Mt or commercial organically modified Mt intercalated with stearylbenzyldimethyl ammonium chloride (Nanofil 2®) and distearyldimethyl ammonium chloride (Nanofil 8®), respectively. The grafting/intercalation of the aminosilane inside the Mt interlayer spaces was studied by means of Fourier transform infrared (FTIR), X-ray diffraction (XRD), nuclear magnetic resonance (NMR) and thermogravimetric analysis (TGA). After isothermal curing at 90°C the Mt epoxy nanocomposites were analyzed by means of XRD and dynamic mechanical analysis (DMA). The glass transition temperature of all prepared nanocomposites containing silylated Mt, is slightly higher than that of the neat epoxy (2 to 5°C). In the presence of 1 to 5m% of silylated Mt in epoxy matrix the storage modulus increases from about 5 to 15% at 25°C, respectively, compared to the pristine epoxy matrix, while only 0-4% increase was observed for epoxy nanocomposites with commercial modified Mt.
Ethylene-vinyl acetate (EVA)/ sepiolite nanocomposites were prepared by melt blending in a twin screw extruder. The structural, morphological, thermal, flammability and mechanical properties of the EVA/sepiolite nanocomposites were investigated using X-ray diffraction (XRD), Fourier transform infrared (FTIR), field emission scanning electron microscopy (FESEM), thermal analysis, tensile properties and limiting oxygen index (LOI) measurements. X-ray diffraction analysis and FESEM revealed good dispersion of sepiolite in EVA matrix. The tensile strength of EVA/sepiolite increased by 21% and Young’s modulus increased by 47% at 5wt.% and7wt.% sepiolite content, respectively. The thermal stability and fire retardancy of the nanocomposites improved with sepiolite incorporation.
The effects of sepiolite modified with γ-aminopropyltriethoxylsilane (KH550-Sp) on thermal properties of polyurethane (PU) nanocomposites were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TG), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and tensile test. The DSC results showed that the glass transition temperature of hard segments in PU/KH550-Sp nanocomposite increased with the increase of KH550-Sp, because sepiolite restricted the formation of hydrogen bonding within hard segments of polyurethane. TG results revealed that the thermal stability of PU was improved by KH550-Sp, and the onset decomposition temperature for PU nanocomposites with a KH550-Sp content of 3 wt% was about 20 °C higher than that for pure PU. The tensile properties of pure PU and nanocomposites before and after ageing 120 °C for 72 h were determined, and it was observed that the percentage loss in tensile strength decreased with the addition of KH550-Sp because of an oxidation barrier of KH550-Sp confirmed by ATR-FTIR.
X-ray powder diffraction (XRD), thermal gravimetric analysis (TGA), surface area measurements, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy were used to examine the surface properties of organosilane-modified smectite-type aluminosilicate clays. Organic modified clays derived from the reactions of montmorillonite (containing 93-95% montmorillonite from a bentonite, <1% quartz, and 4-6% opal CT) with octadecyltrichlorosilane (C{sub 18}H{sub 37}SiCl{sub 3}) and octadecyltrimethoxysilane [C{sub 18}H{sub 37}Si(OMe){sub 3}] are highly hydrophobic. Surface loadings of the modified clays depend on the organosilane and the solvent, and they range from 10 to 25 wt. %. The organic species are probably adsorbed to the outer surfaces and bound to the edges of the clay via condensation with edge-OH groups. Encapsulation of montmorillonite with C{sub 18}H{sub 37}SiCl{sub 3} and C{sub 18}H{sub 37}Si(OMe){sub 3} resulted in hydrophobic coating that acts like a 'cage' around the clay particles to limit diffusion. Basal spacings of the organic modified clays remain at {approx}15 {angstrom} upon heating to 400{sup o}C in N{sub 2}, whereas those of unmodified clays collapse to {approx}10 {angstrom}. A considerable reduction in surface area (by 75-90%) for organic modified clays is observed, which is consistent with the existence of a surface coating. The solvent used can affect the amount of organic silane coated on the clay particles, whereas the difference between the products prepared using C{sub 18}H{sub 37}SiCl{sub 3} and C{sub 18}H{sub 37}Si(OMe){sub 3} in the same solvent is relatively small. The carbon and oxygen K-edge NEXAFS spectroscopy of the modified montmorillonite surfaces showed that surface coatings on the outside of the clay particles exist. The encapsulating system may allow for economical remediation and storage of hazardous materials.
The surface properties of organosilane-modified smectite-type clays were examined by various physico-chemical techniques, including thermal gravimetric analysis (TGA), surface area measurements from N2 adsorption/desorption experiments (BET method), Fourier transform infrared spectroscopy (FTIR), chemical stability measurements in aqueous medium, and elemental analysis. The organically modified clays derived from the reaction of two natural Cameroonian smectites and one standard bentonite sample (for comparison purposes) with γ-aminopropyltriethoxysilane and 3-mercaptopropyltrimethoxysilane. Efficiency of the grafting process was demonstrated by comparing the physico-chemical characteristics of the clays before and after reaction with the organosilanes, which resulted in decreased porosity and decreased amounts of surface hydroxyl groups concomitantly to the presence of aminopropyl or mercaptopropyl groups attached to the aluminosilicate structure. The amine-bearing materials were subject to rather low chemical stability in neutral aqueous medium, which was improved with decreasing pH, while the thiol-containing ones were found to be stable over a wide pH range (2–10). Possible use of these materials as adsorbents for mercury(II) species was discussed and some preliminary experiments based on carbon paste electrodes modified with such grafted clays highlighted their interest for electroanalytical applications.
Purpose
The purpose of this paper is to investigate the effect of different PHS on the surface chemistry of fumed silica treated with aminopropyltrimethoxysilane (APTMS).
Design/methodology/approach
The reaction conditions involved variation of pH ranging from acidic to alkaline. Different analytical techniques including FT‐IR spectroscopy, thermogravimetric analysis (TGA), CHN and Zeta potential analyses were employed to investigate the surface chemistry of treated particles. In addition, the stability of silanised silica dispersions were studied using turbidimetric and rheometric measurements.
Findings
It was revealed that in all conditions silica was more or less chemically grafted by the silane. When the pH of treating bath was adjusted to 1‐2 prior and during the reaction, 58 percent grafting was observed, as obtained by CHN and TGA analyses. At very alkaline conditions, however, the grafting content declined to 29 percent. The variations in grafting were dependent on the silane hydrolysis and its further condensation with the silica surface. Zeta potential measurements showed a drastic change from −7.1 mv to +18.01 mv (at pH 7) for the untreated particle and the one with the highest grafting, respectively. The dispersion stability of differently treated particles varied in solvents with different Hansen solubility parameters (HSP). Moreover, due to the variations of surface chemistry of particles, their rheological behaviours were significantly influenced.
Originality/value
The results obtained in this work showed that the surface chemistry of fume silica could be tuned with treating method. The highest content of grafting led to a better dispersion in solvents having greater hydrogen bonding component and to an inferior dispersion in solvents with higher polar component.
Adsorption of neutral organic molecules and the monovalent organic cations methylene blue (MB) and crystal violet (CV) to sepiolite was determined experimentally and investigated by an adsorption model. The largest amounts of MB and CV adsorbed were about 4-fold of the cation exchange capacity (CEC) of sepiolite. Consequently, it was proposed that most of the above described adsorption was to neutral sites of the clay. The adsorption model considered combines the Gouy-Chapman solution and specific binding in a closed system. The model was extended by allowing cation adsorption to neutral sites of the clay, in addition to adsorption to negatively charged sites and adsorption to neutral complexes formed from 1 cation adsorbed to a negative surface site. The amount of available neutral sites was determined from the adsorption of the neutral molecule Triton-X 100 (TX100). The model could adequately simulate the adsorption of the neutral molecules TX100 and crown ether 15-crown-5 (15C5) as well as the organic cations. Due to aggregation of MB molecules in solution, their adsorption was somewhat less than that of CV at the larger added concentrations. A consideration of the molecular dimensions of TX100, MB and CV suggested that their adsorption was mostly to external sites of the clay and that their entry to the sepiolite channels was largely excluded. This interpretation is supported by infrared spectroscopy (IR) measurements, which show large perturbations of the peak corresponding to vibrations of external Si-OH groups of the clay and confirm complete occupancy of external sites by MB and CV.
We report in this work the grafting of laponite clay particles with monofunctional c-methacryloxypropyl dimethyl methoxy silane (c-MPTDES) and trifunctional c-methacryloxypropyl trimethoxy silane (c-MPTMS) coupling agents. The evolution of the grafted amount and of the grafting yield was monitored as a function of the reaction time and of the initial silane concentration. We showed that the grafted amount increased with time and with the silane content up to a plateau value. The amount of chemisorbed silane at saturation varied from 0.56 to 1.9 mmol g 21 depending on the nature of the coupling agent, the reaction time and the grafting conditions. While the trifunctional silane was capable of both reaction with the clay edges and formation of complex polysiloxane oligomers in the bulk which were further deposited on the particulate surface, the monofunctional silane formed a monolayer coverage on the border of the clay plates with the carbonyl groups being directed toward the surface as attested by Fourier transform infrared (FTIR) spectroscopy. The properties of the organosilane-modified laponite were examined by various analytical techniques such as wide-angle X-ray diffraction (WAXD), nitrogen adsorption and thermogravimetric analysis (TGA). The monofunctional silane exhibited nearly no effect on the physicochemical properties of the clay whereas grafting of the trifunctional silane resulted in decreased porosity, increased interlamellar distance and higher hydrophobicity.
We present the first surfactant-free inverse emulsion polymn. by using organically modified clay platelets as stabilizers. Colloidally stable inverse Pickering emulsions of aq. acrylamide (AAm) or 2-hydroxyethyl methacrylate (HEMA) in cyclohexane stabilized by hydrophobic Cloisite 20A (MMT20) were prepd. With both oil-sol. 2,2'-azobis(isobutyronitrile) (AIBN) and water-sol. 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] (VA-086) as initiators, inverse latexes in the size range of 700-980 nm were successfully obtained. It has been revealed by SEM and cryo-TEM that the latexes were stabilized by hydrophobic clays, as exemplified by the rugged surface of the particles. It was shown from thermogravimetric anal. (TGA) that all the clay platelets were incorporated into the composite particles, and in partially exfoliated state as indicated by X-ray diffraction study. [on SciFinder(R)]
Sepiolite has been treated with some organosilanes including dimethyloctadecylchlorosilane (DMODCS), dimethyldichlorosilane (DMDCS), and 3-aminopropyltriethoxysilane (3-APT). FTIR measurements have been used to discuss the interactions between sepiolite surface and organosilane molecules. The disappearance of OH stretching peaks of sepiolite has shown the strong interactions between the surface and organosilane molecules. H-bonds have also been indicated by the frequency shifts of OH stretching vibrations. The changes in the electrokinetic properties of the treated sepiolite samples have been investigated by following the zeta potential of the particles as a function of pH. The treatment of sepiolite with 3-APT causes a shift of isoelectronic point (IEP) from 7.8 to 9.7, to a more basic value compared to sepiolite itself. DMODCS and DMDCS-treated sepiolite samples have, however, been found to have isoelectronic points in more acidic region than that of sepiolite, which are 5.2 and 5.6, respectively.
This work investigates the graft polymerization of acrylic acid onto nanoclay platelets to be utilized as reinforcing fillers in an experimental dental adhesive. Physical and mechanical properties of the adhesive and its shear bond strength to dentin are studied. The effect of the modification on the stability of the nanoparticle dispersion in the dilute adhesive is also investigated.
Poly(acrylic acid) (PAA) was grafted onto the pristine Na-MMT nanoclay (Cloisite(®) Na(+)) through the free radical polymerization of acylic acid in an aqueous media. The resulting PAA-g-nanoclay was characterized using FTIR, TGA and X-ray diffraction (XRD). The modified nanoclays were added to an experimental dental adhesive in different concentrations and the morphology of the nanoclay layers in the photocured adhesive matrix was studied using TEM and XRD. Shear bond strength of the adhesives containing different filler contents was tested on the human premolar teeth. The stability of nanoclay dispersion in the dilute adhesive was also studied using a separation analyzer. The results were then statistically analyzed and compared.
The results confirmed the grafting reaction and revealed a partially exfoliated structure for the PAA-g-nanoclay. Incorporation of 0.2 wt.% of the modified nanoclay into the experimental adhesive provided higher shear bond strength. The dispersion stability of the modified nanoparticles in the dilute adhesive was also enhanced more than 25 times.
Incorporation of the modified particles as reinforcing fillers into the adhesive resulted in higher mechanical properties. The nanofiller containing bonding agent also showed higher shear bond strength due to the probable interaction of the carboxylic acid functional groups on the surface of the modified particles with hydroxyapatite of dentin.
The interaction of water with the clay fractions (<2 micrometer) from two midwestern soils was studied using Fourier transform infrared (FTIR) spectroscopy and gravimetric methods. The soil clay fractions were obtained from a Blount loam (fine, illitic, mesic Aeric Epiaqualfs) and a Fayette silty clay loam (fine-silty, mixed, mesic, superactive Typic Hapludalfs). These clay fractions were exchanged with Mg(2+), 50:50 Ca(2+)/Mg(2+), Ca(2+), Na(+), and K(+) to determine the influence of the exchangeable cation on their water sorption behavior. Water sorption isotherms and FTIR spectra of the clays were collected simultaneously using a gravimetric-spectroscopic cell. Overall, the amount of water sorbed by the samples increased as the ionic potential of the exchangeable cation increased and was strongly correlated to the hydration energy of the cations (P > F < 0.0001). The position of the H-O-H bending band (v2 mode) also increased with increasing ionic potential of the exchangeable cation indicating strengthening of water H bonds. In addition, it was observed that the position of this band decreased with increasing water content for the Mg-exchanged clays compared with an overall increase for the Ca-exchanged samples. X-ray diffraction patterns indicated an expansion of the phyllosilicate clay minerals as the water activity increased; however, no differences were observed between the Ca- and Mg-exchanged samples. This study shows that the molecular properties of water on Ca- and Mg-exchanged soil clays are similar to that on specimen clays and provides new insight about the role of exchangeable cations in soils.
Novel poly(ether-imide) and sepiolite nanocomposites were synthesized based on a unique diamine monomer with the aim of improving physical and mechanical properties of final polyimide films. The diamine was polycondensed with 4,4′-(hexafluoroisopropylidene) diphthalic anhydride to produce related poly(ether amic acid) prepolymer. Pure poly(ether-imide) and nanocomposite films were prepared via thermal imidization process of poly(ether amic acid). Coexistence of ether, pyridine, and phenylene functional groups in the diamine chemical structure resulted in flexible polyimide films with significant thermal, physical, and mechanical properties. Thermal stability, glass-transition temperature, dimensional stability, and tensile properties of polymer and nanocomposites were studied and compared. Morphology of nanocomposites was also investigated using scanning and transmission electron microscopic methods to study the distribution and dispersion behavior of sepiolite nanofibers in the polyimide matrix. By introduction of sepiolite nanoparticles, overall improvement of properties was observed in respect to pure polyimides. Copyright © 2015 John Wiley & Sons, Ltd.
Polynorbornene/sepiolite hybrid nanocomposite films were prepared using polynorbornene dicarboximide and modified sepiolite with 3- aminopropyltriethoxysilane (3-APTES). Exo-N-(3,5- dichlorophenylnorbornene)-5,6-dicarboxyimide (monomer) and their copolymers were synthesized via ring-opening polymerization using ruthenium catalysts. Subsequently, the surface modified sepiolite by 3-APTES was mixed with the polynorbornene copolymers to prepare the hybrid nanocomposite films. The modified sepiolite particles were well-dispersed in N,N-dimethylacetamide (DMAc) and distributed randomly throughout the polynorbornene matrix in the hybrid films, which enhanced the dimensional stability, mechanical and oxygen barrier properties of the polynorbornene/sepiolite hybrid nanocomposite films.
Novel sepiolite-based poly(amide-imide) nanocomposites were prepared by in-situ polymerization via polycondensation of a diamine containing amide groups with hexafluoropropane dianhydride. The process involved dispersion of sepiolite in poly(amic acid) solution followed by thermal imidization to get ultimate nanocomposites. The morphology, thermal and mechanical performances of nanocomposites with various sepiolite contents were studied. Nanoparticles were homogenously dispersed throughout the matrix with 50–65 nm size range. Due to such dispersion, poly(amide-imide)-sepiolite nanocomposite films exhibited improvements on the thermal-mechanical properties. The best results arose from favorable miscibility between polymer and sepiolite in the nanocomposites when 3 wt.% nanoparticles were introduced into poly(amide-imide) matrix.
Clay mineral containing kaolinite, illite and montmorillonite was organofunctionalized with silylating agents: (3-aminopropyl)triethoxysilane, 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane and (3-mercaptopropyl)trimethoxy-silane, to yield three hybrids labelled Clay1, Clay2 and Clay3, respectively. These solids were characterized using elemental analysis, thermogravimetry, X-ray diffractometry, infrared spectroscopy, scanning electron micrograph, and 29Si and 27Al solid state NMR. Immobilized quantities of the organic groups were 0.66 mmol g−1, 0.48 mmol g−1 and 0.88 mmol g−1 for Clayx (x = 1–3), respectively. X-ray diffraction patterns confirmed the immobilization of silanes onto the surface without changes in the textural properties of the clay mineral as noted from the SEM images. Spectroscopic measurements were in agreement with the covalent bonding between the silanes and the hydroxyl groups deposited on the surface. The new hybrids were utilized as adsorbents of cobalt in aqueous solution, with retention values of 0.78 mmol g−1, 1.1 mmol g−1 and 0.70 mmol g−1 for Clayx (x = 1–3), respectively.
Polylactide-based nanocomposites containing unmodified and organic modified sepiolite were prepared through a solution casting method. The structure and properties of materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). From the results it can be concluded that the bundles of sepiolite have been dispersed into small aggregates containing several nanorods without destroying the crystal structure. Sepiolite nanofibers were well dispersed in the PLA matrix, exhibiting a randomly orientation with the contact among them in all cases. But the thermal stability of nanocomposites has been improved more by introducing unmodified sepiolite than that with organic modified sepiolite, which has also been confirmed by molecular dynamics simulation results that hydrophobic parts of organic modifiers could prevent the interaction between PLA molecules and sepiolite surface.
Infrared spectra of silane coupling agents deposited on E-glass fiber were obtained by Fourier transform infrared spectroscopy (FT-IR). A spectral subtraction technique resolved all vibrational modes of the coupling agent deposited from various concentrations of treating solutions. The amount of vinyl functional coupling agent was determined by measuring the integrated peak intensities of the organic functional group. It revealed that the thickness of the coupling agent layer on the glass fiber depended on the concentrations of the treating solution. The rates of condensation reaction of polysiloxanol with and without glass fiber were followed. The coupling agent on the glass fiber reacted much faster than without glass at room temperature. It was concluded that the coupling agent molecules near the glass fiber surface have some order and can easily participate in the condensation reaction. The carbonyl group of a methacryl functional silane hydrogen bonds with hydroxyl groups. The methacryl functional silane on the glass fiber showed less hydrogen bonded groups than the precipitated polysiloxanol suggesting a mechanism of predominant head-to-head adsorption.
Biocompatible gelatin foams were found to exhibit significantly improved mechanical properties by the additions of sepiolitenanofibres. Gelatin nanocomposite foams containing various contents of sepiolite were prepared by lyophilization. With the presence of 9.1 wt% sepiolite, the Young's modulus and compressive collapse strength of the gelatin foam with a cell size of 159 μm and a porosity of 98% were increased by 288% and 308%, respectively. Such enhancements were attributable to the strong interactions between hydrophilic gelatin and sepiolite as suggested by the results from Fourier transform infrared spectroscopy and differential scanning calorimetry which show substantial shifts in the characteristic absorption peaks and the glass transition temperature, to the reduced cell sizes characterised by scanning electron microscopy, and to the reinforcement effects of sepiolite on the gelatin solid material. The mechanical properties of the low-density closed-cell gelatin/sepiolite nanocomposite foams were well predicted using the Gibson–Ashby model for open cells after normalisation of the Young's modulus of the neat polymer foam.
The availability of the structural micropores in sepiolite for
the access of molecular or ionic entities is an old and controversial subject,
which is revised in this work in the light of the most recent experimental
data obtained in our research group. In this way evidence of the accessibility
of molecules, voluminous ions and polymeric species to the intracrystalline
tunnels of the mineral is presented on the bases of the application of several
techniques to the study of the mineral adsorption properties.
In this paper, we present the first attempt to correlate structure and thermal properties of sepiolite based composites.Composites were prepared in a Brabender internal mixer with 3wt.% of pristine or organically modified sepiolites in two different polymer matrices, polypropylene (PP) and poly (butylene terephthalate) (PBT). Characterization of the materials was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).A nucleating action was found in both polymeric matrices. Furthermore, PP-composites showed interesting features in the polymer crystalline structure. A linear correlation between TONSET and the intensity ratio of PP-composites diffraction peaks (I/II) could be observed.Despite a catalytic effect induced by pristine sepiolite on PP thermal degradation, this drawback could be reduced by sepiolite surface modification. Moreover, higher stability towards thermoxidation was achieved. On the other end, the thermal behaviour of PBT was not affected by the presence of sepiolite.
In this paper the study of the morphological and thermal characterisation of pristine and organically modified sepiolites is performed. Sepiolites modified by means of two functionalization processes were studied: adsorption, of quaternary ammonium salts or amines, or grafting of silane reagents. By means of XRD the characteristic diffraction peaks of sepiolite structure were observed in every sample confirming that no structural changes occurred in the mineral lattice upon functionalization. As sepiolite is a non swelling clay organophilization takes place mainly by surface modification, maintaining its crystalline structure. SEM and HRTEM confirmed that the typical acicular morphology of sepiolite was maintained after modification, although the organically modified needles show a more irregular surface pattern. The study of the thermal behaviour of the organically modified sepiolites was performed by thermogravimetric analysis which shows a complex multi-step degradation process due to the overlapping of sepiolite dehydration processes and organic modifier volatilization.
The structural changes of sepiolite under thermal treatment, and their reversibility, have been examined by thermogravimetry. These changes have been related to the textural changes, determined by N2 adsorption under similar conditions. The folding of this material starts at 390°C, from this temperature the microporosity of the material disappears. This folding is reversible, becoming permanent at 570°C. From 390 to 570°C the surface area remains stable, corresponding to the external surface area of the mineral.
Bound water of sepiolite dehydrates in two steps in the temperature range of 250-650~ as shown in the TG-curve. These steps are described here as steps II and III. At step II, half of the bound water is removed; other half at step III. From step II to IlL discontinuous changes are confirmed in such properties as activation energy of dehydration, a-dimension, axial ratio, and intensities and spacings of X-ray powder reflections. A structural state at step II may be recognized as a distinct phase in the dehydration process.
A new bio-based elastomer synthesized from soybean oil was filled with nanoclay to generate an elastic nanocomposite. A solubility parameter study was used to select the organoclay for poly(acrylated oleic methyl ester) (AOME). Effects of the nanoclay on the macroscopic and microscopic properties were explored. The morphology varies from fully exfoliated to intercalated structure with different types of clay and clay concentrations. Mechanical properties are significantly improved by the addition of organoclays. The elongation at break increases as well as the tensile strength. A decrease in the crosslink density of this elastic nanocomposite, measured by swelling test, indicates that the clay hinders chemical crosslinking and also confirms the formation of physical crosslinks. Percolation studies show the improvement of the network structure by nanoclays. The onset of the thermal decomposition was hindered by the loading of the nanoclay. Clay effects on biodegradability were studied as well.
Two kinetics studies with regard to isothermal and nonisothermal crystallization were conducted on composites samples containing polypropylene and sepiolite surface-treated with isobutyric acid. Comparison of both studies allows us to demonstrate that isobutyric acid-treated sepiolite incorporated to the polypropylene at different ratios acts as an effective nucleating agent and, due to its surface activity, generates two different crystalline structures, one of which is attributable to the formation of a mesophase on the periphery of the sepiolite particle.
Surface modification of clay minerals plays an important role for their application as fillers for polymeric materials. Among the many modification reactions, the silanization reaction uses alkoxysilanes and exploits the OH reactive sites of the montmorillonite structure. We found that using an excess of silane it is possible to functionalize the clay mineral and, at the same time, to intercalate some monomers or oligomers into the clay mineral galleries, greatly enhancing the interlayer distance. The montmorillonite modified in this way has been then used in the preparation of nanocomposite coatings by mixing it with a photocurable epoxy matrix. After UV irradiation the coatings obtained were submitted to morphological, thermal and mechanical analysis. The photopolymerization kinetics was also investigated. The introduction of the modified montmorillonite allowed to obtain transparent nanocomposite coatings characterized by a mixed intercalated/exfoliated structure and better thermal and scratch resistance performances in comparison with the montmorillonite free coatings.
Poly(vinyl chloride) (PVC)/sepiolite nanocomposites were
prepared using PVC and natural, organo-modified, acid–activated, and calcined
sepiolite samples through the solution intercalation method. Thermogravimetric
(TG) analysis, UV–vis spectrophotometry, Fourier transform infrared
spectroscopy, and scanning electron microscopy were used to determine the
thermal stability, optical behavior, interactions, and morphology of samples,
respectively. The dispersion of sepiolite in the PVC matrix was examined by
X-ray diffraction (XRD) and transmission electron microscopy (TEM). The
nanocomposites exhibited higher thermal stability than that of pure PVC. XRD
and TEM results showed that sepiolite particles were dispersed in the nanoscaled
PVC matrix. The UV–vis spectra showed that the transmission of nanocomposites
increased with the sepiolite content and wavelength. The thermal degradation
behavior of PVC was investigated by using TG analysis under nonisothermal
conditions at different heating rates under a nitrogen atmosphere. The apparent
activation energy of samples was determined by using the Kissinger method. The
nanocomposite showed higher activation energy than that of pure PVC. Theresults showed that the thermal degradation of PVC was shifted toward higher
temperatures with an increase in the amount of sepiolite.
Mono- and trifunctional organo alcoxysilane derivatives carrying a terminal reactive methacryloyl group have been used as reagents for the chemical modification of synthetic Laponite clay platelets in toluene. Qualitative evidence of the presence of chemically attached silane molecules was provided by Fourier transform infrared and 29Si and 13C solid-state NMR spectroscopies. Quantitative data (grafted amount and grafting yield) were also obtained by means of elemental and thermogravimetric analysis. While the trifunctional coupling agent was grafted on the clay edges in the form of oligomers pillaring the clay stacks, the monofunctional derivative selectively attached to the individual clay sheets as confirmed by X-ray diffraction and Brunauer−Emmett−Teller measurements. In agreement with these findings, only the clay stacks grafted using the monofunctional coupling agent could be satisfactorily redispersed into water. The aqueous suspensions of the grafted colloidal disks were characterized by small-angle X-ray scattering, dynamic light scattering, and cryogenic transmission electron microscopy. Emulsion copolymer latexes, the surface of which was decorated by individual Laponite platelets, were finally produced using the grafted clay particles as seeds. This new method provides an efficient way for constructing water-based polymer/exfoliated clay nanocomposites.
Intumescent flame-retardant polypropylene-containing phosphorus and nitrogen compounds were enhanced significantly by adding a small amount of sepiolite as a synergistic agent. The flame-retardant polypropylene composite was characterized by limiting oxygen index (LOI), UL-94, the cone calorimeter (CCT), and thermogravimetric analysis (TGA) to study the combustion behavior and thermal stability. The addition of 0.5% sepiolite increased the LOI from 29.8 to 31.8. The addition of sepiolite at a low additive amount appears to be an optimum blend ratio for the low heat release rate, total smoke, and CO2 production. Sepiolite also has a significant improvement in mechanical properties.
The first examples of thermoset polyurethane-clay nanocomposites have been prepared by curing a polyurethane network in the presence of alkylammonium-exchanged forms of montmorillonite. A unique stress-strain behavior was observed for the elastomeric nanocomposites. The reinforcement effects of the silicate nanolayers not only greatly improved the tensile properties of the matrix but the strain-at-break also increased with increasing clay loading. Thus, nanocomposite formation both strengthens and toughens the elastomeric matrix compared to the pristine polymer.
We report in this paper the synthesis and characterization of a new class of biopolymer−clay nanocomposites based in the assembling of chitosan to sepiolite, which is a natural magnesium silicate showing a microfibrous texture. CHN and ICP/AES chemical analyses, XRD, FTIR spectroscopy, 13C solid-state NMR, LT-SEM, and thermal analysis have been employed in the characterization of the resulting nanocomposites. The adsorption isotherm of chitosan on sepiolite in acidic medium reveals a significant coverage of the biopolymer at high equilibrium concentration values indicating a multilayer adsorption. The arrangement of chitosan chains on the surface of the silicate microfibers is discussed on the basis of physicochemical data obtained by application of the different techniques. The potentiometric response of this new type of bio-nanocomposites incorporated in carbon paste electrodes toward aqueous salt solutions was employed for the first time as a valuable technique for a rapid assessment of the ion-exchange behaviors. Thermal behaviors and mechanical properties have been determined by DTA-TG and DMTA, respectively. As these materials are well-processed as self-supporting films, in view of their properties they show potential interest as membranes for different processes related to separation of ions and gases, as well as components in electrochemical devices (fuel-cell, potentiometric sensors).
The process of incorporation of pyridine in the nanostructured tunnels of sepiolite was studied in detail, using various complementary characterization techniques, microporosimetry, thermal gravimetric analysis, FTIR, and multinuclear solid-state NMR. It is demonstrated that a remarkable nanohybrid material, SEP−PYR, is formed through the direct coordination of pyridine to the edge Mg(II) sites of the tunnels. This material is formed at temperatures above 140 °C when the sepiolite tunnels are dehydrated and the pyridine molecules are trapped in the tunnels. In a first step toward the formation of SEP−PYR, the pyridine molecules were incorporated at room temperature in the tunnels, by exposing sepiolite to pyridine vapors. The incorporated pyridine molecules are H-bound to the structural water molecules coordinated to the edge Mg(II) cations. In a second step, upon heating to 140 °C, approximately 50% of the pyridine is lost, together with most of the structural water coordinated to Mg(II). This event is accompanied by direct coordination of the remaining pyridine molecules in the tunnels to the edge Mg(II) ions of the octahedral sheets, resulting in a material with a structure similar to the parent sepiolite, but with pyridine molecules coordinated to the Mg(II) edge cations. This material is stable up to 450 °C. At this temperature, the coordinated pyridine molecules escape from the tunnels, resulting in a collapsed sepiolite structure.
Nanocomposites are prepared from Na-montmorillonite and poly(ethylene oxide) or poly[oxymethylene oligo(oxyethylene)] and characterized by X-ray diffraction, impedance spectroscopy, DTA, and TGA. Two ordered phases with intersheet spacings of 13.6 and 17.7 angstrom, accommodating either single or double polymer layers within the montmorillonite galleries, are formed with polymer/Na-montmorillonite stoichiometries of 0.15 and 0.30 g/g, respectively. Materials prepared with intermediate stoichiometries yield diffraction profiles characteristic of solid solutions of these two phases. The details of composition and structure provide strong evidence that the polymer conformation is not helical as in crystalline PEO but more closely resembles an adsorbed layer. Sodium salts such as NaClO4 can also be incorporated into the polyether/clay phases. The double-layer phase exhibits a maximum stable ionic conductivity between 10(-5) and 10(-6) S cm-1 at 520 K.
Poly(ethyl methacrylate) (PEMA) and poly(2-hydroxyethyl methacrylate) (PHEMA) nanocomposites with sepiolite in pristine and silylated form were prepared using the solution intercalation method and characterized by the measurements of XRD, TEM, FTIR-ATR, TG/DTG, and DSC. The TEM analysis indicated that the volume fraction of fibers in sepiolite decreased and the fiber bundles dispersed in PEMA and PHEMA at a nanometer scale. These results regarding TEM micrographs were in agreement with the data obtained by XRD. The increase in thermal stability of nanocomposites of PEMA is higher than that of PHEMA according to the data obtained from TG curves. The DTG analysis revealed that sepiolite/modified sepiolite caused some changes, as confirmed by FTIR in the thermal degradation mechanism of the polymers. Tg temperatures of PEMA and PHEMA usually increased upon the addition of sepiolite/modified sepiolite. In addition, modification of sepiolite with 3-APTS had a slight influence on thermal properties of the nanocomposites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers
Epoxy nanocomposites containing rod‐like silicate (attapulgite) were prepared using a simple organic modification to the nanorods. The modification led to effective interfacial adhesion between the ceramic nanorods and the epoxy resin and hence good load transfer. Scanning electron microscopy examination revealed a uniform dispersion of nanorods in the epoxy resin. Compared to the neat resin, nanocomposites with 7.47 vol.‐% nanorods exhibited an increase in the (rubbery state) storage modulus of 122.5%. In addition, the nanocomposites exhibited improved dimensional stability both above and below the T g .
Storage modulus of the neat resin and nanocomposites.
magnified image Storage modulus of the neat resin and nanocomposites.
A silica xerogel was synthesized from a clay mineral by a new approach using a pillaring method combined with a selective leaching method. Preparation was conducted by applying an HCl/ethanol treatment after intercalation and condensation of tetraethoxysilane (TEOS) and/or methyltriethoxysilane (MTS) into cetyltrimethylammonium (CTA) ion-exchanged vermiculite. The products are porous nanocomposites consisting of TEOS and/or MTS-derived polysiloxane and hydrated silica, resulting from the selective leaching process of the inorganic constituents and the extraction of CTA ions from CTA-exchanged vermiculite after the intercalation of TEOS and/or MTS. The morphology remains similar to the originated vermiculite owing to the topotactic dissolution process. The products have high porosity with 1205–715 m2 g−1 of BET surface area when prepared with up to 2 mol dm−3 HCl concentration. The pore size distributions of the products show a wide distribution from 1 nm to 4 nm in diameter due to the presence of micropores and mesopores. The HCl concentration dependence of the surface area suggests that the main porosity arises from the porous polysiloxane which is formed by the pillaring process. Water adsorption isotherms reveal that the products have a hydrophilic surface originating from silanol groups on the polysiloxane and the hydrated silica. However, the incorporation of MTS in the pillaring process results in successful surface modification of the products. This novel approach is advantageous for the synthesis of highly porous xerogels with different kinds of surface properties.
Hemicelluloses represent a largely unutilized resource for future bioderived films in packaging and other applications. However, improvement of film properties is needed in order to transfer this potential into reality. In this context, sepiolite, a fibrous clay, was investigated as an additive to enhance the properties of rye flour arabinoxylan. Composite films cast from arabinoxylan solutions and sepiolite suspensions in water were transparent or semitransparent at additive loadings in the 2.5-10 wt % range. Scanning electron microscopy showed that the sepiolite was well dispersed in the arabinoxylan films and sepiolite fiber aggregation was not found. FT-IR spectroscopy provided some evidence for hydrogen bonding between sepiolite and arabinoxylan. Consistent with these findings, mechanical testing showed increases in film stiffness and strength with sepiolite addition and the effect of poly(ethylene glycol) methyl ether (mPEG) plasticizer addition. Incorporation of sepiolite did not significantly influence the thermal degradation or the gas barrier properties of arabinoxylan films, which is likely a consequence of sepiolite fiber morphology. In summary, sepiolite was shown to have potential as an additive to obtain stronger hemicellulose films although other approaches, possibly in combination with the use of sepiolite, would be needed if enhanced film barrier properties are required for specific applications.
Organically modified montmorillonites (‘organo-montmorillonites’) have attracted a great deal of interest because of their wide applications in industry and environmental protection. We have synthesized organo-montmorillonites using montmorillonites with different cation exchange capacities (CEC) and surfactants with different alkyl chain number and chain length. The organo-montmorillonites were characterized by X-ray diffraction (XRD) and differential thermogravimetry (DTG). The basal spacing of the organo-montmorillonites increased with surfactant loading, while the maximum basal spacing increased as the alkyl chain length of the surfactant increased. For the same surfactant, the maximum basal spacing of the organo-montmorillonites was little influenced by the CEC of the montmorillonite component. The level of surfactant loading required to reach the maximum basal spacing, however, strongly depended on the CEC. For a given alkyl chain length, the maximum basal spacing increased when the chain number increased from one to two. These findings are important to the preparation of low-cost organoclays for industrial applications.
Monomolecular coverage of mineral particulates by hydrolyzed γ-methacryloxypropyltrimethoxysilane (γ-MPS) has been produced and characterized by diffuse reflectance Fourier transform infrared spectroscopy. Monolayer species are identified by hydrogen bonding interactions between the organofunctionality and the surface functionality. In the monomolecular layer, adsorbed γ-MPS occupies a surface area of 0.59 nm2 per molecule and is oriented parallel to the surface. This value compares closely with an area of 0.55 nm2 per molecule calculated from the spacefilling projection of the molecule interacting with the surface through its silanol and carbonyl functionalities. The adsorbed molecules are densely packed and the molecular orientation appears to be controllable by the method of application.
A series of sepiolites, palygorskites and “Rocky Mountain Leather” (RML) clay minerals have been analysed by controlled rate thermal analysis and differential scanning calorimetry (DSC). Eight weight loss steps are observed and are structure and composition dependent. Three dehydration steps and five dehydroxylation steps are observed. The mass spectrometric curve mimicked the differential thermogravimetric (DTGA) curve enabling the detailed determination of the dehydration and dehydroxylation steps.
The study evaluates properties of an experimental dental composite consisting of a porous thermally sintered nano-silica as filler. The properties are compared with those of an experimental composite containing micro fillers and a commercially available nano-composite, Filtek Supreme(®) Translucent. Different models are used to predict the elastic modulus and strength of the composites.
Nano-silica with primary particles of 12 nm was thermally sintered to form nanoporous filer particles. The experimental composites were prepared by incorporating 70 wt.% of the fillers into a mixture of Bis-GMA and TEGDMA as matrix phase. Having added photoinitiator system the composites were inserted into the test molds and light-cured. The microfiller containing composites were also prepared using micron size glass fillers. Degree of conversion (DC%) of the composites was measured using FTIR spectroscopy. Diametral tensile strength (DTS), flexural strength, flexural modulus and fracture toughness were measured. SEM was utilized to study the cross section of the fractured specimens. The surface topography of the specimens was investigated using atomic force microscopy (AFM). The specific surface area of the sintered nano silica was measured using BET method. The data were analyzed and compared by ANOVA and Tukey HSD tests (significance level=0.05).
The results showed improvements in flexural modulus and fracture toughness of the composites containing sintered filler. AFM revealed a lower surface roughness for sintered silica containing composites. No significant difference was observed between DTS, DC%, and flexural strength of the sintered nanofiller composite and the Filtek Supreme(®). The results also showed that the modulus of the composite with sintered filler was higher than the model prediction.
The thermally sintered nano-porous silica fillers significantly enhanced the mechanical properties of dental composites introducing a new approach to develop materials with improved properties.
Surface modification reactions on needle-like sepiolite using alkyl and functional silanes have been carried out in the form of aqueous gels. In contrast with modifications in organic solvents, reactions in water make it possible to modify the surface of almost-individual sepiolite fibers and produce either a continuous coating or a nanotexturization of the sepiolite fiber surface, depending on the reaction conditions. This clean procedure substitutes advantageously organic solvent surface modifications and allows the tuning of surface properties such as specific surface area, wetting behavior, and chemical functionalization. A consequence of such tuning is, for example, the excellent dispersion of modified sepiolite nanofibers in a great variety of polymers by routine compounding and processing techniques.
In this work, the silylation of sodium montmorillonite (Na-MMT) was performed in glycerol using 3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and 3-[2-(2-aminoethylamino)ethylamino]-propyl-trimethoxysilane. The effects on the d-spacing of sodium montmorillonite (Na-MMT) upon reaction with three aminosilanes of different chain length were studied in details by combining experimental and computational techniques. Infrared spectroscopy was used to monitor the grafting process, while the degree of grafting was calculated using thermogravimetric analysis. X-ray diffraction experiments were carried out to evaluate the shift of the (0 0 1) basal spacing. It was found that the degree of silylation of Na-MMT increases with increasing the length of the aminosilane organic moieties, the overall aminosilane concentration, and temperature. The same beneficial effects were observed on the silicate d-spacing, as its value increases with increasing silane concentration and reaction temperature. Remarkably, however, increasing the length of the organic chains in the silane modifiers resulted in decreasing values of the Na-MMT interlayer distance. A rationale for this behavior is proposed on the basis of atomistic molecular dynamics simulation evidences.